Method and apparatus for transmitting/receiving channels in mobile communication system supporting massive mimo

ABSTRACT

A channel transmission/reception method and an apparatus for transmitting/receiving channels between a base station and a mobile terminal efficiently in a mobile communication supporting massive Multiple Input Multiple Output (MIMO) transmission are provided. The method includes determining a resource to which a Demodulation Reference Signal (DMRS) addressed to a terminal is mapped within a resource block, the DMRS resource being positioned in at least one of a first resource set capable of being allocated for DMRS and a second resource set symmetric with the first resource set on a time axis, and transmitting the DMRS and DMRS allocation information to the terminal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 13/857,555, filed on Apr. 5, 2013, and claimed the benefit under 35U.S.C. §119(e) of a U.S. provisional application filed on Apr. 6, 2012in the U.S. Patent and Trademark Office and assigned Ser. No.61/621,176, the entire disclosure of which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communication system. Moreparticularly, the present invention relates to a method and apparatusfor transmitting/receiving channels between a base station and a mobileterminal efficiently in a mobile communication supporting massiveMultiple Input Multiple Output (MIMO) transmission.

2. Description of the Related Art

The mobile communication system has evolved into a high-speed,high-quality wireless packet data communication system to provide dataand multimedia services beyond the early voice-oriented services.Recently, various mobile communication standards, such as High SpeedDownlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA),Long Term Evolution (LTE), and LTE-Advanced (LTE-A) defined in 3rdGeneration Partnership Project (3GPP), High Rate Packet Data (HRPD)defined in 3rd Generation Partnership Project-2 (3GPP2), and 802.16defined in Institute of Electrical and Electronics Engineers (IEEE),have been developed to support the high-speed, high-quality wirelesspacket data communication services. Particularly, LTE corresponds to acommunication standard developed to support high speed packet datatransmission and to maximize the throughput of the radio communicationsystem with various radio access technologies. LTE-A corresponds to anevolved version of LTE to improve the data transmission capability.

LTE is characterized by 3GPP Release 8 or 9 capable base station andterminal (User Equipment (UE)) while LTE-A is characterized by 3GPPRelease 10 capable base station and UE. As a key standardizationorganization, 3GPP continues standardization of the next release formore improved performance beyond LTE-A.

The existing 3rd and 4th generation wireless packet data communicationsystems (such as HSDPA, HSUPA, HRPD, and LTE/LTE-A) adopt AdaptiveModulation and Coding (AMC) and Channel-Sensitive Scheduling techniquesto improve the transmission efficiency. AMC allows the transmitter toadjust the data amount to be transmitted according to the channelcondition. For example, the transmitter is capable of decreasing thedata transmission amount for bad channel condition so as to fix thereceived signal error probability at a certain level or increasing thedata transmission amount for good channel condition so as to transmitlarge amount of information efficiently while maintaining the receivedsignal error probability at an intended level. Meanwhile, the channelsensitive scheduling allows the transmitter to serve the user havinggood channel condition selectively among a plurality of users so as toincrease the system capacity as compared to allocating a channel fixedlyto serve a single user. This increase in system capacity is referred toas multi-user diversity gain. In brief, the AMC method and thechannel-sensitive scheduling method are methods for receiving partialchannel state information being fed back from a receiver, and applyingan appropriate modulation and coding technique at the most efficienttime determined depending on the received partial channel stateinformation.

In a case of using AMC along with MIMO transmission scheme, it may benecessary to consider a number of spatial layers and ranks fortransmitting signals. In this case, the transmitter determines theoptimal data rate in consideration of the number of layers for use inMIMO transmission.

Recent research aims to replace Code Division Multiple Access (CDMA)used in the legacy 2nd and 3rd mobile communication systems withOrthogonal Frequency Division Multiple Access (OFDMA) for the nextgeneration mobile communication system. The 3GPP and 3GPP2 are in themiddle of the standardization of OFDMA-based evolved system. OFDMA isexpected to provide superior system throughput as compared to the CDMA.One of the main factors that allow OFDMA to increase system throughputis the frequency domain scheduling capability. As channel sensitivescheduling increases the system capacity using the time-varying channelcharacteristic, OFDM can be used to obtain more capacity gain using thefrequency-varying channel characteristic.

As described above, LTE supports MIMO using a plurality of transmit andreceive antennas. MIMO corresponds to a technique for transmittinginformation multiplexed spatially in adaptation to instantaneouschannels established with plural transmit and receive antennas. The MIMOtransmission is capable of multiplexing plural data streams spatiallyonto a single time-frequency resource so as to be able to increase thedata rate a few folds as compared to the non-MIMO transmission. LTERelease 11 supports the MIMO transmission with up to 8 transmit antennasand up to 8 receive antennas. In this case, up to 8 data streams can bemultiplexed spatially, resulting in increase of data rate up to 8 timesmore than non-MIMO transmission.

Typically, MIMO is classified into one of Single-User MIMO (SU-MIMO) fortransmitting spatially multiplexed multiple data streams to a singleuser and Multi-User MIMO (MU-MIMO) for transmitting spatiallymultiplexed multiple data streams to multiple users.

In contrast to the SU-MIMO transmitting the spatially multiplexedmultiple data streams to a single UE, the MU-MIMO is capable oftransmitting the spatially multiplexed multiple data streams to multipleUEs. In the MU-MIMO, the evolved Node B (eNB) transmits plural datastreams such that each UE is capable of receiving one or more of thedata streams transmitted by the eNB. Accordingly, the MU-MIMO isadvantageous especially when the number of eNB's transmit antennas isgreater than the number of UE's receive antennas.

In the case of SU-MIMO, the maximum number of data streams capable ofbeing multiplexed spatially is restricted by min(NTx, NRx) where NTxdenotes the number of eNB's transmit antennas and NRx denotes the numberof UE's receive antennas. Meanwhile, in the case of MU-MIMO, the maximumnumber of data streams capable of being multiplexed spatially isrestricted by min(NTx, NMS X NRx) where NMS denotes the number of UEs.

Massive MIMO or Full Dimension MIMO is an emerging technology feasiblewith a few dozen to a few hundred of eNB's transmit antennas. Thus, inorder to enhance the system throughput, it is required to increase thenumber of data streams significantly as compared to the legacy LTEsystem. In order to accomplish this, the massive MIMO transmissionscales up the MU-MIMO for simultaneous transmission to multiple UEs byan order of magnitude.

Therefore, a need exists for a channel transmission/reception method andapparatus capable of allocating Demodulation Reference Signal (DMRS)resource guaranteeing orthogonality among a plurality of UEs in themassive MIMO system

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problem and/or disadvantages and to provide at least theadvantages described below. Accordingly, an aspect of the presentinvention is to provide a channel transmission/reception method andapparatus capable of allocating Demodulation Reference Signal (DMRS)resource guaranteeing orthogonality among a plurality of User Equipments(UEs) in the massive Multiple Input Multiple Output (MIMO) system.

In accordance with an aspect of the present invention, a channeltransmission method of a base station in a mobile communication systemsupporting massive MIMO is provided. The method includes determining aresource to which a DMRS addressed to a terminal is mapped within aresource block, the DMRS resource being positioned in at least one of afirst resource set capable of being allocated for DMRS and a secondresource set symmetric with the first resource set on a time axis, andtransmitting the DMRS and DMRS allocation information to the terminal.

In accordance with another aspect of the present invention, a channelreception method of a terminal in a mobile communication systemsupporting massive MIMO is provided. The method includes receiving DMRSallocation information from a base station, and determining a resourceto which the DMRS addressed to the terminal is mapped within a resourceblock, a DMRS resource being positioned in at least one of a firstresource set capable of being allocated for DMRS and a second resourceset symmetric with the first resource set on a time axis.

In accordance with another aspect of the present invention, a channeltransmission apparatus of a base station in a mobile communicationsystem supporting massive MIMO is provided. The apparatus includes atransceiver which transmits and receives signals and data to and from aterminal, and a controller which controls determining a resource towhich a DMRS addressed to a terminal is mapped within a resource block,the DMRS resource being positioned in at least one of a first resourceset capable of being allocated for DMRS and a second resource setsymmetric with the first resource set on a time axis.

In accordance with another aspect of the present invention, a channelreception apparatus of a terminal in a mobile communication systemsupporting massive MIMO is provided. The apparatus includes atransceiver which transmits and receives signals and data to and from abase station, and a controller which controls determining a resource towhich the DMRS addressed to the terminal is mapped within a resourceblock, a DMRS resource being positioned in at least one of a firstresource set capable of being allocated for DMRS and a second resourceset symmetric with the first resource set on a time axis.

In accordance with another aspect of the present invention, a channeltransmission method of a base station in a mobile communication systemsupporting massive MIMO is provided. The method includes determiningresources to which DMRS addressed to a terminal is mapped within atleast one resource block, a number of the DMRS resources beingdetermined based on a number of consecutive resource block on afrequency in a subframe scheduled for downlink data transmission to theterminal, and transmitting the DMRS to the terminal.

In accordance with another aspect of the present invention, a channelreception method of a terminal in a mobile communication systemsupporting massive MIMO is provided. The method includes receivingdownlink scheduling information from a base station, and receiving DMRSon the DMRS resources of which number allocated in a resource block isdetermined based on a number of consecutive resource block on afrequency in a subframe scheduled for downlink data transmission to theterminal.

In accordance with another aspect of the present invention, a channeltransmission apparatus of a base station in a mobile communicationsystem supporting massive MIMO is provided. The apparatus includes atransceiver which transmits and receives signals and data to and from aterminal, and a controller which controls determining resources to whichDMRS addressed to a terminal is mapped within at least one resourceblock, a number of the DMRS resources being determined based on a numberof consecutive resource block on a frequency in a subframe scheduled fordownlink data transmission to the terminal, and transmitting the DMRS tothe terminal.

In accordance with still another aspect of the present invention, achannel reception apparatus of a terminal in a mobile communicationsystem supporting massive MIMO is provided. The apparatus includes atransceiver which transmits and receives signals and data to and from abase station, and a controller which controls receiving downlinkscheduling information from a base station and DMRS on the DMRSresources of which number allocated in a resource block is determinedbased on a number of consecutive resource blocks on a frequency in asubframe scheduled for downlink data transmission to the terminal.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram illustrating a time-frequency resource structure ofLong Term Evolution (LTE)/Long Term Evolution-Advanced (LTE-A) systemaccording to an exemplary embodiment of the present invention;

FIG. 2 is a diagram illustrating a Resource Block (RB) for a subframe asa minimum quantum of resource for downlink scheduling in an LTE/LTE-Asystem to an exemplary embodiment of the present invention;

FIG. 3 is a diagram illustrating an evolved Node B (eNB) with MassiveMultiple Input Multiple Output (MIMO) capability to multiple UserEquipments (UEs) in a mobile communication system according to anexemplary embodiment of the present invention;

FIG. 4 is a diagram illustrating a Demodulation Reference Signal (DMRS)structure for a Massive MIMO transmission according to an exemplaryembodiment of the present invention;

FIG. 5 is a diagram illustrating exemplary structures of an RB with aDMRS pattern for use in a transmission method according to an exemplaryembodiment of the present invention;

FIGS. 6A to 6C are diagrams illustrating three formats of DemodulationReference Signal (DMRS) allocation information for use in a transmissionmethod according to an exemplary embodiment of the present invention;

FIG. 7 is a flowchart illustrating an eNB procedure of determining DMRSallocation for massive MIMO and indicating DMRS allocation informationto a UE in a transmission method according to an exemplary embodiment ofthe present invention;

FIG. 8 is a diagram illustrating exemplary structures of an RB with aDMRS pattern for use in a transmission method according to a secondexemplary embodiment of the present invention;

FIG. 9 is a diagram illustrating exemplary structures of an RB withPhysical Downlink Shared Channel (PDSCH) and DMRS from a viewpoint of aUE in a transmission method according to an exemplary embodiment of thepresent invention;

FIG. 10 is a flowchart illustrating a procedure of configuring DMRSresource size through higher layer signal from an eNB to a UE andallocating DMRS group and DMRS port(s) based on a configuration in atransmission method according to the second exemplary embodiment of thepresent invention;

FIG. 11 is a flowchart illustrating a procedure of determining aconstant value specified in a mobile communication standard as a DMRSresource size in a transmission method according to an exemplaryembodiment of the present invention;

FIG. 12 is a diagram illustrating exemplary structures of an RB withDMRS for use in a transmission method according to an exemplaryembodiment of the present invention;

FIG. 13 is a diagram illustrating resources with DMRSs for explainingDMRS density depending on frequency resources allocated consecutively ina transmission method according to an exemplary embodiment of thepresent invention;

FIG. 14 is a diagram illustrating a subframe with multiple frequencyregions carrying Physical Downlink Control Channel (PDCCH) addressed toa UE in a transmission method according to an exemplary embodiment ofthe present invention;

FIG. 15 is a diagram illustrating a subframe with multiple frequencyregions carrying PDCCH addressed to a UE in a transmission methodaccording to an exemplary embodiment of the present invention;

FIG. 16 is a flowchart illustrating an eNB's adaptive DMRS densitydetermination procedure of a transmission method according to anexemplary embodiment of the present invention;

FIG. 17 is a flowchart illustrating a UE's adaptive DMRS densitydetermination procedure of a transmission method according to anexemplary embodiment of the present invention;

FIG. 18 is a block diagram illustrating a configuration of an eNBapparatus according to an exemplary embodiment of the present invention;and

FIG. 19 is a block diagram illustrating a configuration of a UEapparatus according to an exemplary embodiment of the present invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

Although the description is directed to the Orthogonal FrequencyDivision Multiple Access (OFDM)-based radio communication system,particularly the 3rd Generation Partnership Project (3GPP) EvolvedUniversal Terrestrial Radio Access (EUTRA), it will be understood bythose skilled in the art that the present invention can be applied evento other communication systems having the similar technical backgroundand channel format, with a slight modification, without departing fromthe spirit and scope of the present invention.

FIG. 1 is a diagram illustrating a time-frequency resource structure ofLong Term Evolution (LTE)/Long Term Evolution-Advanced (LTE-A) systemaccording to an exemplary embodiment of the present invention.

Referring to FIG. 1, the radio resource is divided into Resource Blocks(RBs) in the frequency domain and subframes in the time domain. An RBcomprises 12 subcarriers corresponding to the bandwidths of 18 kHz.Meanwhile, a subframe comprises 14 OFDM symbols corresponding to 1 msectime duration. In the LTE/LTE-A system, the resource scheduling isperformed in a unit of a subframe in the time domain and in a unit of anRB in the frequency domain.

FIG. 2 is a diagram illustrating an RB for a subframe as a minimumquantum of resource for downlink scheduling in an LTE/LTE-A systemaccording to an exemplary embodiment of the present invention.

Referring to FIG. 2, the radio resource corresponds to one subframe inthe time domain and one RB in the frequency domain. As aforementioned,an RB comprises 12 subcarriers in the frequency domain and 14 OFDMsymbols (e.g., total 168 time-frequency positions). In the LTE/LTE-Asystem, each time-frequency position is referred to as Resource Element(RE).

With the radio resource structured as shown in FIG. 2, a number ofdifferent signals as follows are transmitted:

1. Cell Specific Reference Signal (CRS): Transmitted for all UserEquipments (UEs) to receive within a cell.

2. Demodulation Reference Signal (DMRS): Transmitted to a specific UEfor channel estimation to recover the information on Physical DownlinkShared Channel (PDSCH). A DMRS resource or port is transmitted with theapplication of the same precoding linked thereto. A UE scheduled toreceive on a specific layer of PDSCH receives the DMRS port linked tothe corresponding layer for channel estimation and then recovers theinformation on the corresponding layer based on the estimation result.

3. PDSCH: Used for downlink data transmission from the evolved Node B(eNB) to the UE on the REs with the exception of the REs to which thereference signals are mapped in the data region of FIG. 2.

4. Channel Status Information Reference Signal (CSI-RS): Transmitted tothe UEs within one cell for use in channel state measurement. Aplurality of CSI-RS can be transmitted within a cell.

5. Other control channels (e.g., Physical Hybrid-ARQ Indicator Channel(PHICH), Physical Control Format Indicator Channel (PCFICH), PDCCH, andthe like): Used for the UE to transmit the control information necessaryfor receiving PDSCH or Hybrid Automatic Repeat Request (HARQ) ACK/NACKcorresponding to the uplink data transmission.

In addition to the above signals, zero power CSI-RS can be configured inorder for the UEs within the corresponding cells to receive the CSI-RSstransmitted by different eNBs in the LTE-A system. The zero power CSI-RS(muting) can be mapped to the positions designated for CSI-RS, and theUE receives the traffic signal skipping the corresponding radio resourcein general. In the LTE-A system, the zero power CSI-RS is referred to asmuting. The zero power CSI-RS (muting) by nature is mapped to the CSI-RSposition without transmission power allocation.

Referring to FIG. 2, the CSI-RS can be transmitted at some of thepositions marked by A, B, C, D, E, F, G, H, I, and J according to thenumber of number of antennas transmitting CSI-RS. Also, the zero powerCSI-RS (muting) can be mapped to some of the positions A, B, C, D, E, F,G, H, I, and J. The CSI-RS can be mapped to 2, 4, or 8 REs according tothe number of the antenna ports for transmission. For two antenna ports,half of a specific pattern is used for CSI-RS transmission; for fourantenna ports, entire of the specific pattern is used for CSI-RStransmission; and for eight antenna ports, two patterns are used forCSI-RS transmission. Meanwhile, although the zero power CSI-RS (muting)can be applied to multiple pattern, the zero power CSI-RS cannot beapplied to a part of one pattern if the positions are not overlappedwith CSI-RS position.

In the Multi-User MIMO (MU-MIMO), the number of UEs for simultaneoustransmission is closely related to the downlink DMRS structure. Thedownlink DMRS aims to provide the UE with the channel estimationinformation for use in recovering information carried on PDSCH. Asaforementioned, the DMRS is precoded along with the PDSCH in the LTEsystem such that the UE is capable of using the channel estimation valueacquired through the channel estimation on the DMRS for decoding PDSCH.

For example, the channel estimation on the DMRS should be guaranteed tosome extent to make it possible to recover the PDSCH. This means that KUEs receiving data in MU-MIMO transmission should have the DownLink (DL)DMRSs channel estimation capabilities to some extent in order to receivePDSCHs.

The LTE system is designed to transmit plural DMRSs. In order to usemultiple DMRS ports on the same radio resource in MU-MIMO, a scramblingfunction is provided to secure orthogonality or interferencerandomization among the DMRS ports. In a LTE Release 11 system, DMRSports 7 and 8 may be used in MU-MIMO transmission. In order to secureorthogonality between the DMRS ports 7 and 8, the DMRSs are spread withdifferent orthogonal codes on the time axis so as to be transmitted atthe DMRS transmission positions as shown in FIG. 2. The eNB is capableof randomizing the interference between DMRSs by applying differentscrambling codes to the per-UE DMRSs transmitted at the same positions.Typically, when allocating DMRS resources to two UEs, the channelestimation performance with the orthogonal DMRS resource allocation issuperior to the channel estimation performance with non-orthogonal DMRSresource allocation.

As described above, LTE Release 11 is capable of utilizing up to twoorthogonal DMRS resources (DMRS ports 7 and 8). For example, theorthogonal DMRS resource allocation is applicable for only the MU-MIMOtransmission to two UEs. If the number of UEs for MU-MIMO transmissionis three or more, the orthogonality among the DMRS resources is notguaranteed and thus differentiation among the DMRSs relies onscrambling. For this reason, MU-MIMO transmission is performed up to twoUEs in the real LTE system.

FIG. 3 is a diagram illustrating an eNB with Massive Multiple InputMultiple Output (MIMO) capability to multiple UEs in a mobilecommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 3, the eNB transmits signals to a plurality of UEsthrough multiple transmit antennas as denoted by reference number 300(e.g., through antenna array 300). The multiple transmit antennas can beconfigured as a 2-Dimentional (2D) antenna array panel structure inwhich the antennas 310 are arranged with a distance corresponding to thewavelength function therebetween. With the antenna array 300, the eNB iscapable of a high order MU-MIMO transmission. The high order MU-MIMOtransmission corresponds to transmission of data with the transmissionbeams 320 and 330 separate spatially to plural UEs using multiple eNBs'transmit antennas. The high order MU-MIMO is advantageous in improvingthe system throughput dramatically with the same time and frequencyresource.

In order to accomplish the high order MU-MIMO for simultaneoustransmission to plural users with the same time and frequency resources,an appropriate DMRS structure is necessary as described above. Theappropriate DMRS structure corresponds to the DMRS structureguaranteeing orthogonality among plural UEs in the high order MU-MIMOtransmission. The legacy LTE/LTE-A Release 11 guaranteeing orthogonalitybetween DMRS ports for up to two UEs has to be extended in capacity tooptimize the throughput of the Massive MIMO system with moreorthogonality-guaranteed DMRS ports. The orthogonality-guaranteed DMRSports are the DMRS port resources orthogonal in frequency, time, or codesuch that the corresponding DMRS port or data signal and other users'DMRS ports or data signals do not interfere to each other. Theorthogonality-guaranteed DMRS ports are advantageous in that the per-UEchannel estimation based on DMRS port can be performed withoutinterference of the signal transmitted to other UEs.

FIG. 4 is a diagram illustrating a DMRS structure for a Massive MIMOtransmission according to an exemplary embodiment of the presentinvention.

The DMRS structure of FIG. 4 comprises four DMRS groups. In FIG. 4, theDMRS groups 1 and 2 correspond to the legacy DMRSs 410 defined forallocating DMRS in the legacy LTE/LTE-A system, and the DMRS groups 3and 4 are new DMRSs 400 proposed in an exemplary embodiment of thepresent invention.

Each DMRS group is capable of supporting up to 4 orthogonal DMRS ports.Therefore, up to 16 orthogonal DMRS ports can be realized in theproposed DMRS structure of FIG. 4. Accordingly, up to 16 UEs can bescheduled simultaneously in the MU-MIMO transmission.

According to an exemplary embodiment of the present invention, the fourDMRS ports of each DMRS group are allocated orthogonal code sequences toguarantee the orthogonality therebetween. For example, the four DMRSports of a DMRS group can be allocated the orthogonal code sequences asshown in Table 1.

TABLE 1 DMRS port 1 Orthogonal Code Sequence 1: [+1, +1, +1, +1] DMRSport 2 Orthogonal Code Sequence 1: [+1, −1, +1, −1] DMRS port 3Orthogonal Code Sequence 1: [+1, +1, −1, −1] DMRS port 4 Orthogonal CodeSequence 1: [+1, −1, −1, +1]

As shown in Table 1, each code sequence is made up of four symbols. Foreach DMRS port, the four symbols are transmitted on the 4 OFDM symbolsof the same subcarrier. Each DMRS port is precoded with the sameprecoding as that of the data signal with which it is intended for asdescribed above.

In Table 1, the code sequences of length 4 are used to differentiateamong up to 4 orthogonal DMRS ports of each DMRS group. According to anexemplary embodiment of the present invention, the code sequence oflength 2 can be used to acquire up to two DMRS ports instead of the codesequences of length 4. According to such an exemplary embodiment of thepresent invention, because the length of each sequence code is 2, eachcode sequence repeats twice on the four OFDM symbols of the samesubcarrier. The code sequence of length 2 reduces the number oforthogonal DMRS ports but allocates relatively large amount of radioresource to the corresponding port and thus takes advantage in channelestimation performance. In the case of using the orthogonal codesequence of length 2, it is possible to support up to 8 orthogonal DMRSports.

Also, the orthogonal code sequences of length 2 and length 4 can be usedtogether. For example, the DMRS ports transmitted in the four DMRSgroups as shown in FIG. 4 can use the orthogonal code sequences oflength 2 and length 4 selectively. In this case, the number ofsupportable orthogonal DMRS ports is in the range from 8 to 16.

Referring to FIG. 4, the legacy DMRS resource 410 and the newly proposedDMRS resource 400 are arranged symmetrically. For example, the legacyDMRS resource 410 is symmetrical with the new DMRS resource 400 withrespective to the time axis and, especially, the symmetric axis is thecenter of a subframe. This formation is advantageous to use the samechannel estimator for estimating channels with DMRS ports on the twoDMRS resources.

The DMRS structure of FIG. 4 has the following characteristics:

Up to 16 orthogonal DMRS ports can be utilized;

All of the 16 orthogonal DMRS ports have the same pattern. The patternof any DMRS group can be obtained by applying a time/frequency shift tothe pattern of any other DMRS group; and

The new DMRS 400 is symmetric to the legacy DMRS 410.

As described above, the large number of orthogonal DMRS ports isadvantageous in realizing efficient MU-MIMO transmission for largenumber of UEs. Also, the symmetry of the DMRS resources andtime/frequency shift-based DMRS arrangement are advantageous inminimization of the DMRS channel estimator implementation complexity.

In order to utilize the DMRS structure of FIG. 4, it may be necessary tonotify the co-scheduled UEs of the DMRS structure. For example, thenetwork should indicate to the UEs which DMRS ports to use.

The DMRS port information sent a UE changes in every transmission, andthe number of DMRS ports can change depending on the scheduling decisionof the eNB. For example, the UE may be allocated the DMRS port 1 at theith subframe and DMRS ports 3 and 4 at the (i+1)^(th) subframe. In thisway, the DMRS port allocation is performed depending on the schedulingdecision of the eNB and radio resource distribution. Although at least 8DMRS ports should be utilized for the MU-MIMO transmission to 8 UEs inthe massive MIMO system, the number of DMRS ports can be changed if thenumber of UEs increases or decreases.

According to an exemplary embodiment of the present invention, threemethods for notifying the co-scheduled UEs of DMRS port allocation areproposed. In the following, descriptions are made of the threenotification methods with the exception of other signals such as CRS andCSI-RS. It is assumed that CRS and CSI-RS are transmitted on the radioresource configured by the eNB.

In the first exemplary embodiment of the present invention, the eNBnotifies the UE of the DMRS port allocation through physical layersignaling. For example, the eNB notifies each UE of the DMRS allocationinformation including at least one of the following information throughphysical layer signaling:

A size of DMRS resource in transport block to be transmitted to UE;

An allocated DMRS group; and

An allocated DMRS port(s) within the allocated DMRS group.

FIG. 5 is a diagram illustrating exemplary structures of an RB with aDMRS pattern for use in a transmission method according to an exemplaryembodiment of the present invention.

Referring to FIG. 5, the activated DMRS group corresponds to theresource capable of DMRS allocation in the size of DMRS resources.

According to exemplary embodiments of the present invention, the UE iscapable of determining the total resource allocated for DMRStransmission based on the DMRS resources information included in theDMRS allocation information. The size of the DMRS resources may includethe DMRS resource for the DMRS port transmission to other co-scheduledUEs as well as the DMRS resource for the DMRS port transmission to aspecific UE. The UE is also capable of determining the REs to which theDMRS ports allocated to the UE are mapped among the radio resourcesallocated for DMRS based on the DMRS group notification. If the notifiedDMRS resource size is larger than the size of the DMRS resourcesallocated to itself, the UE assumes that the DMRS or data transmissionis muted on the DMRS resource not allocated to the UE. In addition, theUE is capable of determining the code resource used for DMRS porttransmission to the UE based on the indication of allocated DMRS port inthe assigned DMRS group.

The DMRS resource size, assigned DMRS group, and allocated DMRS portincluded in the DMRS allocation information are notified to the UE assummarized in Tables 2 and 3.

TABLE 2 Code Point Indication Information Element 1: 00 DMRS resourcesize = 1 DMRS group Indicate the size of the 01 DMRS resource size = 2DMRS groups DMRS resources (2 bits) 10 DMRS resource size = 3 DMRSgroups 11 DMRS resource size = 4 DMRS groups Information Element 2: 00UE assigned DMRS group 1 Indicate the allocated 01 UE assigned DMRSgroup 2 DMRS group (2 bits) 10 UE assigned DMRS group 3 11 UE assignedDMRS group 4 Information Element 3: 00 UE assigned DMRS port 1 Indicatethe allocated within assigned DMRS group DMRS port within the 01 UEassigned DMRS port 2 DMRS group (2 bits) within assigned DMRS group 10UE assigned DMRS port 3 within assigned DMRS group 11 UE assigned DMRSport 4 within assigned DMRS group

TABLE 3 Code Point Indication Information Element 1: 00 DMRS resourcesize = 1 DMRS Indicate the size of the group (DMRS Group 1) DMRSresources (2 bits) 01 DMRS resource size = 2 DMRS groups (DMRS Group 1,2) 10 DMRS resource size = 3 DMRS groups (DMRS Group 1, 2, 3) 11 DMRSresource size = 4 DMRS groups (DMRS Group 1, 2, 3, 4) InformationElement 2: 00 UE assigned DMRS group 1 Indicate the allocated 01 UEassigned DMRS group 2 DMRS group (2 bits) 10 UE assigned DMRS group 3 11UE assigned DMRS group 4 Information Element 3: 000 UE assigned DMRSport 1 Indicate the allocated within assigned DMRS group DMRS portwithin the 001 UE assigned DMRS port 2 DMRS group (3 bits) withinassigned DMRS group 010 UE assigned DMRS port 3 within assigned DMRSgroup 011 UE assigned DMRS port 4 within assigned DMRS group 100 UEassigned DMRS port 1, 2 within assigned DMRS group 101 UE assigned DMRSport 3, 4 within assigned DMRS group 110 UE assigned DMRS port 1, 2, 3within assigned DMRS group 111 UE assigned DMRS port 1, 2, 3, 4 withinassigned DMRS group

In the DMRS allocation indication methods based on Tables 2 and 3, theUE determines the size of the entire DMRS resource based on theinformation element 1 and the DMRS group allocated to the UE based onthe information element 2. The UE assumes that the DMRS and PDSCHtransmission are muted on the radio resource of other DMRS groups withthe exception of the DMRS group indicated by the information element 2among the DMRS resource indicated by the information element 1.

Although it is assumed that one UE is allocated only one DMRS group inTables 2 and 3, plural DMRS groups can be allocated to a UE in the sameway. Finally, the UE is capable of determining the allocated DMRS portin the assigned DMRS group based on the information element 3.

The above three DMRS allocation informations (DMRS resource size,assigned DMRS group, and allocated DMRS port) can be notified to the UEindependently or in the aggregated format through joint encoding.

FIGS. 6A to 6C are diagrams illustrating three formats of DMRSallocation information for use in a transmission method according to anexemplary embodiment of the present invention.

Referring to FIG. 6A, the format of transmitting informationsindividually based on Tables 2 and 3 is provided. For example, the threeinformation and other DL scheduling information are transmitted in therespective information elements 600, 610, 620, 630.

Referring to FIG. 6B, the format of transmitting the DMRS sizeinformation, the jointly encoded DMRS group and DMRS port assignmentinformation, and other downlink scheduling informations in therespective information elements 640, 650, and 660, is provided.

Referring to FIG. 6C, the format of transmitting the jointly encodedDMRS size, DMRS group assignment, and DMRS port allocation informationsin one information element 670 and other downlink scheduling informationin another information element 680, is provided.

FIG. 7 is a flowchart illustrating an eNB procedure of determining DMRSallocation for massive MIMO and indicating DMRS allocation informationto a UE in a transmission method according to an exemplary embodiment ofthe present invention.

Referring to FIG. 7, the eNB performs scheduling to determineco-scheduled UEs at step 700. Scheduling is a process of selecting UEsfor downlink transmission, and the eNB determines the UEs inconsideration of the downlink channel state and data amount. Once theUEs for DL MU-MIMO transmission with the same radio resource have beendetermined at step 700, the eNB determines the size of the DMRS resourcefor transmission to the selected UEs, DMRS group per UE, and DMRSport(s) per UE.

The DMRS allocation information determined at step 700 is transmitted tothe co-scheduled UEs at step 710. The eNB is capable of transmitting theDMRS allocation information through PDCCH or E-PDCCH for physical layercontrol signal transmission in LTE/LTE-A.

At step 720, each UE receives the PDCCH or E-PDCCH transmitted by theeNB and determines the DMRS allocation information addressed thereto.The DMRS allocation information received by the UE includes the DMRSresource size, assigned DMRS group, and allocated DMRS port(s).

The UE assumes, based on the information acquired at step 720, that theradio resource with the exception of the part carrying the DMRSaddressed thereto as the resource used for neither DMRS transmission norPDSCH transmission at step 730. For example, at step 730, the UEestimates a DL channel based on the assigned DMRS ports.

By taking notice of this, the UE determines the REs to which the PDSCHaddressed thereto is mapped and receives the PDSCH thereon at step 740.For example, the UE performs rate matching around DMRS REs signaled tothe UE.

For example, if the UE is notified that the DMRS size is 4 or four DMRSgroups are used in DMRS allocation and DMRS group 2 is assigned to theUE, the corresponding UE attempts receiving data under the assumptionthat the DMRS is received at position in the DMRS group 2 and PDSCH isreceived on the rest radio resource with the exception of the DMRSgroups 1, 2, 3, and 4.

In the DMRS allocation notification procedure according to the secondexemplary embodiment of the present invention, the eNB notifies the UEof the DMRS resource size through higher layer signaling and of theassigned DMRS group and DMRS port(s) through physical layer controlchannel. In this case, the following informations are transmitted to theUE through physical control channel (e.g., PDCCH, Enhanced PhysicalDownlink Control Channel (E-PDCCH), and the like):

Allocated DMRS group; and

Allocated DMRS port(s) within the DMRS group.

In the case in which the UE is notified of the DMRS resource sizethrough higher layer signal and other information through physical layercontrol channel as in the second exemplary embodiment of the presentinvention, it is advantageous to reduce the DL overhead caused by theDMRS-related control information. For example, it may be advantageous toreduce the DL overhead caused by the DMRS-related control informationbecause the control information transmitted through physical layercontrol channel varies frequently, particularly at every 1 msec inLTE/LTE-A, in contrast to the control signal transmitted through higherlayer signal which varies little for relatively long time duration.

However, in the case of the UE is notified of the DMRS resource sizethrough higher layer signaling, dealing with the change of the number ofco-scheduled UEs dynamically is difficult and thus there is a need ofsecuring a sufficiently large DMRS resource. For example, when thenumber of co-scheduled UEs is changed dynamically in the range from 4 to8, the eNB is capable of notifying the UE of the DMRS resource sizesupporting DMRS ports for 8 UEs through higher layer signaling. As aconsequence, the eNB may fail to optimize the DMRS resource sizedepending on the co-scheduled UEs combination, thereby resulting inredundancy or shortage of DMRS resource.

FIG. 8 is a diagram illustrating exemplary structures of an RB with aDMRS pattern for use in a transmission method according to a secondexemplary embodiment of the present invention.

Referring to FIG. 8, the eNB notifies the UE of DMRS resource size=4through higher layer signaling. In this case, the signal can betransmitted on the PDSCH mapped to the radio resource for four DMRSgroup regardless of the number of DMRS group for use in real DMRSallocation, and the DMRS groups not used in real DMRS allocation on thisradio resource are maintained in the state not used as shown in FIG. 8.

In the second exemplary embodiment of the present invention, the DMRSgroup allocation and DMRS port allocation based on the physical layercontrol channel (e.g., PDCCH or E-PDCCH, and the like), can be performedas summarized in Tables 4 and 5.

TABLE 4 Code Point Indication Information Element 2: 00 UE assigned DMRSgroup 1 Indicate the allocated 01 UE assigned DMRS group 2 DMRS group (2bits) 10 UE assigned DMRS group 3 11 UE assigned DMRS group 4Information Element 3: 00 UE assigned DMRS port 1 Indicate the allocatedwithin assigned DMRS group DMRS port within the 01 UE assigned DMRS port2 DMRS group (2 bits) within assigned DMRS group 10 UE assigned DMRSport 3 within assigned DMRS group 11 UE assigned DMRS port 4 withinassigned DMRS group

TABLE 5 Code Point Indication Information Element 2: 00 UE assigned DMRSgroup 1 Indicate the allocated 01 UE assigned DMRS group 2 DMRS group (2bits) 10 UE assigned DMRS group 3 11 UE assigned DMRS group 4Information Element 3: 000 UE assigned DMRS port 1 Indicate theallocated within assigned DMRS group DMRS port within the 001 UEassigned DMRS port 2 DMRS group (3 bits) within assigned DMRS group 010UE assigned DMRS port 3 within assigned DMRS group 011 UE assigned DMRSport 4 within assigned DMRS group 100 UE assigned DMRS port 1, 2 withinassigned DMRS group 101 UE assigned DMRS port 3, 4 within assigned DMRSgroup 110 UE assigned DMRS port 1, 2, 3 within assigned DMRS group 111UE assigned DMRS port 1, 2, 3, 4 within assigned DMRS group

Unlike the DMRS allocation based on Tables 2 and 3, the DMRS allocationbased on Tables 4 and 5 transmits the Information Element(s) indicatingthe allocated DMRS group and allocated DMRS port(s) through the physicallayer control channel but not the Information Element 1 indicating DMRSresource size. Similar to the first exemplary embodiment of the presentinvention, the frequency-time resource for DMRS is determined accordingto the DMRS resource size. The UE assumes that the REs used in DMRStransmission or the REs designated by the indicated DMRS resource sizeare not used for PDSCH transmission to thereto.

FIG. 9 is a diagram illustrating exemplary structures of an RB withPDSCH and DMRS from a viewpoint of a UE in a transmission methodaccording to an exemplary embodiment of the present invention.

Referring to FIG. 9, the UE is notified of the DMRS resource size of 4through higher layer signaling. If one of DMRS groups 1, 2, 3, and 4 isassigned, the corresponding UE assumes that the remaining three DMRSgroups are not used for PDSCH transmission. For example, if the UE isscheduled on the DMRS group 3 in FIG. 9, the UE assumes that the DMRSgroups 1, 2, and 4 are not intended for PDSCH transmission to theretoregardless whether other terminals are scheduled assigned DMRS on theseDMRS groups.

FIG. 10 is a flowchart illustrating a procedure of configuring DMRSresource size through higher layer signal from an eNB to a UE andallocating DMRS group and DMRS port(s) based on a configuration in atransmission method according to the second exemplary embodiment of thepresent invention.

The second exemplary embodiment of the present invention illustrated inFIG. 10 differs from the first exemplary embodiment of the presentinvention illustrated in FIG. 7 in that the procedure is performed inthe order of determining the DMRS resource size at the eNB, notifyingthe UE of the DMRS size, configuring the DMRS size to the UE, andscheduling the UE in FIG. 10 while the DMRS size is notified to the UEafter scheduling the UE in FIG. 7. For example, the UE is configuredwith the DMRS resource size notified through higher layer scheduling andreceives the DMRS group and port allocation information from the eNB onPDCCH or E-PDCCH.

At step 1000, the network configures the size of the DMRS resources(e.g., number of DMRS groups). For example, the eNB configures the sizeof the DMRS resources.

At step 1010, the network performs scheduling to determine co-scheduledUEs. For example, the eNB performs the scheduling to determine theco-scheduled UEs.

At step 1020, the network notifies the UE of DMRS port(s) allocatedthereto via a control channel. For example, the DMRS allocationinformation is transmitted to the co-scheduled UEs. The eNB may transmitthe DMRS allocation (e.g., the DMRS port(s) allocated to the UE) throughPDCCH or E-PDCCH for physical layer control signal transmission inLTE/LTE-A.

At step 1030, the UE receives the control channel. For example, each UEreceives the PDCCH or E-PDCCH transmitted by the eNB and determines theDMRS allocation information addressed thereto.

At step 1040, the UE estimates a DL channel based on assigned DMRSport(s).

At step 1050, the UE performs rate matching around DMRS REs signaled tothe UE. For example, the UE determines the REs to which the PDSCHaddressed thereto is mapped and receives the PDSCH thereon.

In the case of the second exemplary embodiment of the present invention,the UE has no DMRS resource configuration information at the timeinitiating communication with a specific eNB and thus there may be thetime duration with uncertainty on how to assume the DMRS resource size.For example, the UE receives the DMRS resource size configuration fromthe eNB after notifying the eNB that it is the Massive MIMO and supportsDMRS structure as shown in FIG. 4. If the UE does not know the DMRSresource size before receiving the initial DMRS resource sizeconfiguration from the eNB, this causes a problem.

In order to avoid such a problem, an exemplary embodiment of the presentinvention proposes an approach to determine a constant value specifiedin the mobile communication standard as the DMRS resource size. Thismethod is advantageous in handover procedure for a certain UE to movefrom one cell to another.

FIG. 11 is a flowchart illustrating a procedure of determining aconstant value specified in a mobile communication standard as a DMRSresource size in a transmission method according to an exemplaryembodiment of the present invention.

Referring to FIG. 11, the UE initiates handover from cell A to cell B atstep 1100. At this time, the UE takes action differently depending onwhether the UE has the information on the DMRS resource size of the cellB.

At step 1110, the UE determines whether the UE has information on theDMRS resource size of the cell B.

If the UE determines that that the UE has not yet received the DMRSresource size configuration information of cell B at step 1110, the UEproceeds to step 1120 at which the UE assumes the constant valuespecified in the standard as the DMRS resource size and receives theDMRS group and DMRS port(s) allocation information to receive PDSCH.Thereafter the UE ends the process.

Otherwise, if the UE determines that the UE has received the DMRSresource configuration information of cell B through higher layersignaling at step 1110, the UE proceeds to step 1130 at which the UEconfigures the DMRS resource size as signaled and receives the allocatedDMRS group and DMRS port(s) information based on the DMRS resource size.Thereafter, the UE proceeds to step 1140 at which the UE receives PDSCHusing the assigned DMRS port(s) based on the signaled DMRS resourcesize.

In the DMRS allocation information notification procedure according tothe third exemplary embodiment of the present invention, the UE whichhas received the DMRS allocation information assumes that there is noPDCCH transmission addressed thereto on the radio resource with theexception of the DMRS group allocated thereto.

FIG. 12 is a diagram illustrating exemplary structures of an RB withDMRS for use in a transmission method according to an exemplaryembodiment of the present invention.

Referring to FIG. 12, the four RBs with respective DMRS group 1, DMRSgroup 2, DMRS group 3, and DMRS group 4 are provided. The UE is notifiedwhich DMRS group is allocated thereto through physical layer controlchannel or higher layer signaling. The UE assumes that only the DMRSgroup allocated thereto is used for DMRS transmission and the radioresource corresponding to other DMRS groups is used for its PDSCH. Inthe case of allocating a DMRS group with the physical layer controlsignal, the UE receives the DMRS group allocation control signal and theDMRS port allocation control signal from the eNB through physical layersignaling. In the case of transmitting the DMRS group allocation controlinformation to the UE through higher layer signaling, the UE receivesonly the DMRS port allocation control signal using the physical layercontrol signal.

In the third exemplary embodiment of the present invention, the UEassumes that the DMRS resource is constant. As illustrated in FIG. 12,the UE assumes that the radio resource corresponding to only the oneDMRS group allocated to it is used for DMRS transmission.

According to exemplary embodiments of the present invention, there areadvantages associated with improve the system performance of the massiveMIMO system by supporting plural DMRS ports as shown in FIG. 4. In thiscase, however, the DMRS-related downlink overhead is in proportion tothe number of DMRS ports. For example, as the number of orthogonal DMRSports increases, using more downlink radio resource for the orthogonalDMRS ports may be necessary. Because the DMRS and PDSCH are implementedin the set of the same radio resource, if more radio resources are usedfor DMRS transmission, the radio resource for use in PDSCH transmissionis reduced.

In order to overcome the DMRS overhead-related problems, exemplaryembodiments of the present invention propose a structure in which theDMRS density is adjusted according to the number of consecutive RBsallocated to the UE in the frequency domain. The DMRS density denotesthe number of REs used for transmitting a DMRS port within one RB. Forexample, as illustrated in FIG. 4, a DMRS port is transmitted usingtotal 12 REs per RB. The DMRS density is 12 REs/RB in the exampleillustrated in FIG. 4.

The resource configuration proposed in exemplary embodiments of thepresent invention may determine the DMRS density depending on whetherthe PDSCH transmitted to the UE is mapped to K or more consecutive RBswithin a subframe in the frequency domain. For example, according toexemplary embodiments of the present invention, K can be set to acertain value.

If the PDSCH is transmitted on K or more consecutive RBs in thefrequency domain, the UE and the eNB assume a low DMRS density.Otherwise, if the PDSCH is transmitted on a number of the RBs less thanK, the DMRS density is assumed low.

FIG. 13 is a diagram illustrating resources with DMRSs for explainingDMRS density depending on frequency resources allocated consecutively ina transmission method according to an exemplary embodiment of thepresent invention.

Referring to FIG. 13, the number of consecutive RBs allocated to the UEis assumed to be equal to or greater than K=2. As illustrated in FIG.13, the PDSCH addressed to the UE 1 is transmitted on only the first RB.Meanwhile, the PDSCH addressed to the UE 2 is transmitted twoconsecutive RBs (e.g., the second and third RBs). Accordingly, if theadaptive DMRS density determination method proposed in exemplaryembodiments of the present invention is applied, the DMRS for PDSCHaddressed to the UE 1 is transmitted with 12 REs per RB while the DMRSfor PDSCH addressed to the UE 2 is transmitted with 8 REs per RB.

If the PDSCH is transmitted on the consecutive RBs as described above,reducing the DMRS density may be possible because the consecutive RBundergo similar radio channel and thus channel estimation on an RB canbe performed using DMRSs of adjacent RBs. According to the exemplaryembodiment of the present invention illustrated in FIG. 13, similarchannel estimation performances are expected in the following two cases:

Single RB assignment with high DMRS density; and

Multiple consecutive RBs assignment with low DMRS density.

In an LTE communication system, when transmitting PDSCH to a UE,allocating the RBs on multiple frequency regions may be possible. Inthis case, the DMRS density can be determined based on the number ofconsecutive RBs in the frequency domain.

FIG. 14 is a diagram illustrating a subframe with multiple frequencyregions carrying PDCCH addressed to a UE in a transmission methodaccording to an exemplary embodiment of the present invention.

Referring to FIG. 14, the DMRS density is assumed to be reduced with K=2or more consecutive RBs allocated to the UE in the frequency domain.

As illustrated in FIG. 14, the UE receives the PDSCH on the RBs 1410,1430, 1440, 1470, 1480, and 1490. At this time, the eNB and the UEassume high DMRS density to the RBs allocated not consecutively as theRB 1410. In contrast, the UE assumes low DMRS density to the consecutiveRBs such as RBs 1430 and 1440. Likewise, because the RBs 1470, 1480, and1490 are consecutive allocations, the UE assumes low DMRS density tothese three consecutive RBs.

In addition to the number of RBs allocated consecutively as shown inFIG. 14, the DMRS density can be determined based on whether theconsecutive RBs are included in a predetermined region.

FIG. 15 is a diagram illustrating a subframe with multiple frequencyregions carrying PDCCH addressed to a UE in a transmission methodaccording to another exemplary embodiment of the present invention.

Referring to FIG. 15, according to the exemplary embodiment of thepresent invention, the eNB and the UE determine the DMRS density basedon whether the consecutive RBs are included in a specific region as wellas the number of consecutively allocated RBs.

As illustrated in FIG. 15, a PRB group is a set of a predeterminednumber of RBs and, in the case of an LTE system, the PRB group isdetermined according to the system bandwidth. In an exemplary embodimentof the present invention, the low DMRS density is applied when thefollowing condition is fulfilled and, otherwise, the high DMRS densityas depicted in FIG. 15:

K or more consecutive RBs are allocated and the K or more consecutiveRBs include all RBs included in a PRB group.

In the exemplary embodiment of the present invention illustrated in FIG.15, if the DMRS density is determined in unit of PRB group and if theRBs allocated to the UE consecutively include all RBs included in aspecific PRB group, the low DMRS density is applied.

Assuming K=2 and PRG group as shown in FIG. 15, the high DMRS density isapplied to the RBs 1530 and 1540 unlike the case of FIG. 14 in which thelower DMRS density is applied to the RBs 1530 and 1540. In the case ofRB 1570, because the consecutive RBs 1570, 1580, and 1590 are notincluded in the same PRB group, the high DMRS density is applied to theRB 1570. In contrast, the two consecutive RBs 1580 and 1590 is includedin the PRB group 4, the low DMRS density is applied.

FIG. 16 is a flowchart illustrating an eNB's adaptive DMRS densitydetermination procedure of a transmission method according to anexemplary embodiment of the present invention.

Referring to FIG. 16, the eNB's adaptive DMRS density determinationprocedure is illustrated under the assumption that when K or moreconsecutive RBs are allocated to the UE low density DMRS is transmittedto the UE. K can be set to 2 as in the above-described exemplaryembodiment of the present invention or another value.

As illustrated in FIG. 16, the eNB performs scheduling to allocate afrequency resource to a UE at step 1600. For example, the eNB performsscheduling to determine the co-scheduled UEs. According to thescheduling result at step 1600, the eNB determines whether to configurethe DMRS density of the UE depending on whether K or more consecutiveRBs are allocated to the UE at step 1610. For example, if the eNBdetermines that a UE is not assigned K consecutive RBs at step 1610,then the eNB proceeds to step 1620 at which the eNB transmits highdensity DMRS to the UE. Thereafter, the eNB ends the process. Incontrast, if the eNB determines that K or more consecutive RBs areallocated to the UE, the eNB proceeds to step 1630 at which the eNBtransmits low density DMRS to the UE within the corresponding frequencyregion at step 1630.

FIG. 17 is a flowchart illustrating a UE's adaptive DMRS densitydetermination procedure of a transmission method according to anexemplary embodiment of the present invention.

Referring to FIG. 17, the UE's adaptive DMRS density determinationprocedure is illustrated under the assumption that when K or moreconsecutive RBs are allocated to the UE low density DMRS is transmittedto the UE.

As illustrated in FIG. 17, the UE receives the control channel (e.g.,PDCCH or E-PDCCH) from the eNB and determines the downlink frequencyresource on which the PDSCH is transmitted at step 1700.

Thereafter, the UE determines whether the DMRS allocated thereto is lowdensity DMRS or high density DMRS based on the frequency resourceallocated thereto at step 1710. For example, at step 1710, the UEdetermines whether the UE is assigned K consecutive RBs.

If the UE determines that the number of consecutive RBs allocated to theUE is less than K at step 1710, then the UE proceeds to step 1720 atwhich the UE performs channel estimation under the assumption that highdensity DMRS is transmitted. Thereafter, the UE ends the process. Incontrast, if the UE determines that K or more consecutive RBs areallocated to the UE at step 1710, then the UE proceeds to step 1730 atwhich the UE performs channel estimation under the assumption that thelow density DMRS is transmitted in the corresponding frequency region atstep 1730.

FIG. 18 is a block diagram illustrating a configuration of an eNBapparatus according to an exemplary embodiment of the present invention.

Referring to FIG. 18, the eNB may include a controller 1800, a DMRStransmitter 1820, a PDSCH transmitter 1820, and the multiplexer 1830.

The controller 1800 performs scheduling to assign the frequencyresources for PDSCH transmission to UEs. The scheduling can be performedat every subframe. If the controller 1800 determines that a UE is toreceive PDSCH, the DMRS transmitter 1810 generates DMRS for thescheduled UE.

The controller 1800 controls the DMRS transmitter 1810 to generate DMRSbased on the number of orthogonal DMRS ports, the number of DMRSresource sizes, DMRS group per UE, and DMRS port(s) per UE inconsideration of the number of co-scheduled UEs and the number ofconsecutive RBs allocated per UE. At this time, the PDSCH transmitter1820 generates PDSCH, and the multiplexer 1830 multiplexes the DMRS andPDSCH, the multiplexed DMRS and PDSCH being transmitted to the UE.

FIG. 19 is a block diagram illustrating a configuration of a UEapparatus according to an exemplary embodiment of the present invention.

Referring to FIG. 19, the UE may include a demultiplexer 1900, a DMRSchannel estimator 1910, a PDSCH receiver 1920, a controller 1930, and achannel compensator 1940.

The demultiplexer 1900 of the UE demultiplexes the signal received fromthe eNB. At this time, the controller 1930 controls the demultiplexer1900 to demultiplex the received into DMRS and PDSCH based on the DMRSinformation received through PDCCH/E-PDCCH or higher layer signaling.For example, the controller 1930 demultiplexes the DMRS and PDSCH inconsideration of the DMRS resource size, assigned DMRS group, assignedDMRS port, and DMRS density, the DMRS and PDSCH being input to the DMRSchannel estimator 1910 and PDSCH receiver 1930 respectively.

The DMRS channel estimator 1910 performs channel estimation with theinput DMRS to output a channel estimation value to the channelcompensator 1940 to recover PDSCH.

As described above, the channel transmission/reception method andapparatus for use in the mobile communication system supporting MassiveMIMO transmission is capable of increasing the number of UEs to beserved simultaneously and the number of orthogonal DMRSs by securingextra resources for DMRS allocation.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method of a terminal in a mobile communicationsystem, the method comprising: receiving, from a base station, firstinformation on at least one group of a resource for a demodulationreference signal (DMRS) on a higher layer signal; receiving, from thebase station, second information on a resource for a DMRS allocated tothe terminal on a control channel; and receiving, from the base station,downlink data on a data channel based on the first information and thesecond information.
 2. The method of claim 1, wherein the secondinformation comprises information on a group of resource for the DMRSallocated to the terminal and information on a port for the DMRSallocated to the terminal.
 3. The method of claim 1, further comprising:omitting to monitor a physical downlink shared channel (PDSCH) on the atleast one group of the resource for the DMRS other than the resource forthe DMRS allocated to the terminal.
 4. The method of claim 1, furthercomprising: receiving, from the based station, information on a numberof resource group for the DMRS.
 5. The method of claim 1, wherein thedownlink data is scheduled based on the first information and the secondinformation.
 6. A method of a base station in a mobile communicationsystem, the method comprising: transmitting, to a terminal, firstinformation on at least one group of a resource for a demodulationreference signal (DMRS) on a higher layer signal; transmitting, to theterminal, second information on a resource for a DMRS allocated to theterminal on a control channel; and transmitting, to the terminal,downlink data on a data channel based on the first information and thesecond information.
 7. The method of claim 6, wherein the secondinformation comprises information on a group of resource for the DMRSallocated to the terminal and information on a port for the DMRSallocated to the terminal.
 8. The method of claim 6, further comprising:omitting to transmit a physical downlink shared channel (PDSCH) on theat least one group of the resource for the DMRS other than the resourcefor the DMRS allocated to the terminal.
 9. The method of claim 6,further comprising: transmitting, to the terminal, information on anumber of resource group for the DMRS.
 10. The method of claim 6,wherein the downlink data is scheduled based on the first informationand the second information.
 11. A terminal in a mobile communicationsystem, the terminal comprising: a transceiver configured to transmitand receive at least one signal; and a controller coupled to thetransceiver and configured to: receive, from a base station, firstinformation on at least one group of a resource for a demodulationreference signal (DMRS) on a higher layer signal, receive, from the basestation, second information on a resource for a DMRS allocated to theterminal on a control channel, and receive, from the base station,downlink data on a data channel based on the first information and thesecond information.
 12. The terminal of claim 11, wherein the secondinformation comprises information on a group of resource for the DMRSallocated to the terminal and information on a port for the DMRSallocated to the terminal.
 13. The terminal of claim 11, wherein thecontroller is further configured to omit to monitor a physical downlinkshared channel (PDSCH) on the at least one group of the resource for theDMRS other than the resource for the DMRS allocated to the terminal. 14.The terminal of claim 11, wherein the controller is further configuredto receive, from the based station, information on a number of resourcegroup for the DMRS.
 15. The terminal of claim 11, wherein the downlinkdata is scheduled based on the first information and the secondinformation.
 16. A base station in a mobile communication system, thebase station comprising: a transceiver configured to transmit andreceive at least one signal; and a controller coupled to the transceiverand configured to: transmit, to a terminal, first information on atleast one group of a resource for a demodulation reference signal (DMRS)on a higher layer signal, transmit, to the terminal, second informationon a resource for a DMRS allocated to the terminal on a control channel,and transmit, to the terminal, downlink data on a data channel based onthe first information and the second information.
 17. The base stationof claim 16, wherein the second information comprises information on agroup of resource for the DMRS allocated to the terminal and informationon a port for the DMRS allocated to the terminal.
 18. The base stationof claim 16, wherein the controller is further configured to omit totransmit a physical downlink shared channel (PDSCH) on the at least onegroup of the resource for the DMRS other than the resource for the DMRSallocated to the terminal.
 19. The base station of claim 16, wherein thecontroller is further configured to transmit to the terminal,information on a number of resource group for the DMRS.
 20. The basestation of claim 16, wherein the downlink data is scheduled based on thefirst information and the second information.